These, particularly which team a player is playing for, are as correct as Wikipedia can manage. All players have been shown as playing for the team for which they last made an appearance, so, for instance, Joel Campbell is shown as an Olympiacos player, even though he is only on loan for them from Arsenal.
The clubs with the most players are, oddly enough, Bayern Munich and Manchester United with 14 players each. I say oddly because, well Bayern did well this season, but United really didn’t. The United players are from a wide spread of countries (4 from England, 2 from Spain and Belgium and 1 each for Mexico, Holland, Japan, Ecuador, France and Portugal), while Bayern had 7 from Germany, and 1 each from Brazil, Croatia, Holland, Spain, Switzerland, US and Belgium.
Each team has at least one team member playing in that country. All countries except England and Russia have at least 1 player playing for a foreign club. This leads to a very tight diagram, particularly in the middle.
The graph is a lot more cluttered that the Euro 2012 equivalent, possibly because there’s a lot more teams, and possibly because teams in Spain and Italy (for example) have a lot more foreign players from South America and Africa than they do from other parts of Europe.
The communities view is too confused to interpret, because as well as the countries themselves, the clubs with lot of players represented appear as communities in and of themselves.